Semiconductor manufacturing involves the use of process gas which is delivered from a supply of the process gas to the manufacturing tool through a system or apparatus that includes tubing, valves and a pressure regulator, for example. Increased emphasis is being placed on preserving the purity of the process gas as it travels through the delivery apparatus. Significant progress has been made by machining the surfaces in contact with the gas to a very fine finish, leaving out parts that contribute to particulate contamination such as a bias spring within the pressure regulator, and cleaning the delivery apparatus surfaces to insure a very low particle count, e.g. a small number of particles down to a size of 0.02 micron. Contamination of the process gas can adversely affect the quality of the semiconductors being made with the gas, lowering the yield from the manufacturing process.
Valves and pressure regulators for high purity applications have typically used Kel-F type fluorocarbon polymers for seats. Such plastics absorb moisture during valve and pressure regulator manufacture and release it slowly during their use in a dry gas system. Residual moisture levels required are currently less than ten parts per billion. As feature widths in semiconductors become smaller, e.g. less than 0.5 micron, the requirement for drier systems becomes increasingly important. To avoid contamination from moisture, valves and apparatus for delivering process gas for making semiconductors have been proposed which reduce moisture absorption inside the valve or apparatus by the total elimination of plastics and elastomers in contact with the gas being delivered by the valve or apparatus, as in the commonly assigned U.S. patent application Ser. Nos. 08/575,022 and 08/575,021, both filed Dec. 19, 1995 and now U.S. Pat. Nos. 5,755,428 and 5,762,086, respectively.
The accuracy, or lack thereof, with which the process gas can be supplied to the manufacturing tool can also impact the manufacturing process and yield. An improvement in repeatability and accuracy with which the process gas can be supplied to the manufacturing tool can result in higher yields from the manufacturing process. The accuracy of the control valve of a conventional mass flow controller in reproducing a flow value is typically 1/100 of a maximum flow value of a range of flow values over which the flow of gas is controlled by the controller. The resolution sensitivity with this conventional control valve is typically 1/1000 of the maximum flow value of the range of flow values. As feature widths in semiconductors become smaller, e.g. less than 0.5 micron, the need for accuracy of a control valve in reproducing a flow value becomes increasingly important.
An object of the present invention is to provide an improved micro control valve for precisely controlling the flow of gas over a relatively wide range of flow values, and an apparatus and method for making semiconductors with high purity process gas, having improved accuracy in reproducing a flow value of the process gas as compared with conventional control valves, apparatus and methods to thereby improve yields in making semiconductors.
These and other objects of the invention are attained by the improved micro control valve of the invention for precisely controlling the flow of gas over a relatively wide range of flow values. According to a disclosed, preferred embodiment of the invention, the micro control valve comprises means defining an orifice through which gas flow can be controlled, a valve cooperating with means defining an orifice, and a drive means which can be precisely set for effecting precise relative movement between the valve and the means defining an orifice for precisely controlling the flow of gas through the orifice over the relatively wide range of flow values. The means defining an orifice and the valve are configured, and the drive means effects sufficiently precise relative movement between the valve and the means defining an orifice, such that the accuracy of the control valve in reproducing a flow value for a given setting of the drive means is at least 1/1000 of a maximum flow value of the relatively wide range of flow values. That is, the repeatability of the micro control valve of the present invention is an order of magnitude better than the aforementioned conventional control valve in a mass flow controller.
The micro control valve of the invention is further characterized in that a ratio of a maximum flow value to a minimum flow value of the relatively wide range of flow values over which the flow of gas can be accurately controlled, is at least 1000 to 1. The resolution sensitivity of the micro control valve of the invention is also an order of magnitude better than the aforementioned known control valve. That is, the resolution sensitivity of the precise control of the flow gas by the micro control valve of the present invention is at least 1/10,000 of the maximum flow value of a relatively wide range of flow values over which the flow of gas is controlled by the micro control valve.
The drive means in the disclosed embodiments of the micro control valve comprise a driver which can be set to provide a precise rotational motion and a precision screw mechanism for converting the rotational motion of the driver into linear motion in a desired direction for effecting the relative movement between the valve and the means defining an orifice. A flexible coupling, rigid in torsion, is connected between the driver and the screw mechanism for coupling the rotational motion provided by the driver to the screw mechanism. This flexible coupling is preferably a zero-backlash coupling. The flexible coupling is a multiple convolution bellows in the disclosed embodiments. According to the preferred embodiment, the flexible coupling is axially displaced as it rotates for varying the flow of gas over the relatively wide range of flow values, the coupling having a relatively low spring rate to minimize a longitudinal force created by the displacement of the coupling as it rotates for varying the flow of gas. This longitudinal force is overcome by the force from a bias spring of the valve which longitudinally loads the screw mechanism in the direction of the driver to take up play in the screw mechanism for minimizing hysteresis during operation of the control valve.
The control valve further includes means for aligning the screw mechanism in the valve for providing the linear motion in the desired direction. According to the preferred embodiment, the screw mechanism is a differential screw mechanism. In a second embodiment, a single screw mechanism is employed to provide a linear motion of less than or equal to 0.020 inch per complete turn of the rotational motion input from the driver to the screw mechanism.
A flexible metal diaphragm is mounted in a valve body of the micro control valve for movement toward and away from the means defining an orifice. The valve is connected to a central portion of this diaphragm and to the linear motion output of the screw mechanism. Means are provided for clamping the flexible diaphragm at its periphery into gas sealing contact with the valve body. In the disclosed embodiments this provides metal to metal contact between the flexible metal diaphragm and the metal valve body sealing the gas passage through the valve to atmosphere to prevent contamination by inboard leakage thereby maintaining high purity of the process gas.
The orifice which is adjustably throttled by the valve is formed in an insert in the valve body in the disclosed embodiments. The annular orifice linearly extends along an axis. The valve is in the form of a tapered needle projecting from the diaphragm, the valve being elongated in a direction along the axis of the orifice and tapered at a relatively small angle to the axis. The drive means precisely moves the valve along the axis of the orifice relative to the insert for precisely controlling the flow of gas through the orifice over the relatively wide range of flow values. The diaphragm and screw mechanism are accurately aligned in the valve for providing the linear motion in the desired direction along the axis.
A method of the present invention for making semiconductors comprises providing a supply of pressurized process gas for making semiconductors, regulating the pressure of process gas from the supply of process gas and controlling the flow of the pressure regulated process gas to a processing equipment for making semiconductors, wherein the flow of the pressure regulated process gas to the processing equipment is controlled over a relatively wide range of flow values with a continuously variable micro control valve having a driver which can be precisely set, the micro control valve having an accuracy in reproducing a flow value for a given setting of the driver of at least 1/1000 of a maximum flow value of the relatively wide range of flow values. As a result, relatively high yields in semiconductor making are possible. According to the preferred embodiment of the method, the step of precisely setting the driver of the micro control valve is performed by means of a computer for controlling the process gas supplied to the processing equipment.
An apparatus of the invention for making semiconductors comprises a source of process gas used in making semiconductors, a processing equipment for making semiconductors to which the process gas is to be supplied, and a micro control valve of the present invention for precisely controlling the flow of process gas over a relatively wide range of flow values from the source of process gas to the processing equipment for making semiconductors. The micro control valve has an accuracy in reproducing a flow value for a given setting of the drive means of the control valve which is at least 1/1000 of a maximum flow value of the relatively wide range of flow values.
These and other objects, features and advantages of the present invention will become more apparent from the following detailed description of two disclosed embodiments of the present invention illustrated in the accompanying drawings.